Centrifuge slurry supply

ABSTRACT

A centrifuge of the type which has a central slurry feed pipe, a rotating bowl, and a concentric conveyor which includes a tubular shaft with a helix on the outside. The shaft has rectangular openings in the area of the slurry feed with rectangular orifice plates of hardened material fastened inside the shaft. The orifice plate is sealed to the shaft so that it forms a lip, retaining a pool of slurry within the shaft. The orifice plate is also smaller than the opening and overlaps the trailing edge of the opening.

United States Patent [72] inventor John .I. Halloron, Jr.

Lombard, Ill. I21 1 Appl. No. 807,750 I 22 I Filed Mlr. I7. 1969 I45!Patented Nov. l6. 197i I73 1 Assignee Combustion Engineering. Inc.

Windsor, Conn.

[54] CENTRIFUGE SLURRY SUPPLY ll Claims, 4 Drawing Figs.

[52] [1.8. CI 233/7, 233/47 [51] Int. Cl B04b 1/10 [50] Field of Search233/7. 46, 6. 3, I0. 20. 28

[56] References Cited UNITED STATES PATENTS 3.368.747 2/1968 Lavanchy233/7 lliilll 3.428.248 2/1969 Andresen 3,447,742 6/l969 ErikssonPrimary Examiner- Robert W. Jenkins Arrorneys-Carlton F. Bryant. EldonH. Luther. Robert L. Olson. John F. Carney. Richard H. Berneike. EdwardL. Kochey. Jr. and Lawrence P. Kessler ABSTRACT: A centrifuge of thetype which;has a central slurry feed pipe. a rotating bowl. and aconcentric conveyor which includes a tubular shaft with a helix on theoutside. The shaft has rectangular openings in the area of the slurryfeed with rectangular orifice plates of hardened material fastenedinside the shaft. The orifice plate is sealed to the shaft so that itforms a lip. retaining a pool of slurry within the shaft. The orificeplate is also smaller than the opening and overlaps the trailing edge ofthe opening.

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BY 51 A/O'LL7 ATTORNEY PAIENTEUuuv 1619M 3,620,442

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INVENTOQ Jomv .I HALLORAN I2.

A TT'OENE Y CENTRIFUGE SLURRY SUPPLY BACKGROUND OF THE INVENTION Thisinvention relates to centrifuges for separating solids from liquids andin particular to an arrangement for feeding the slurry into the rotatingbowl of a centrifuge.

ln centrifuges of the type contemplated, the bowl rotates at high speedto develop the centrifugal force which separates the liquid and solids.Within this rotating bowl a conveyor is rotated also at high speed, butat a speed varying slightly from that of the bowl. A helix on theoutside of the conveyor operates to urge the solids towards the solidsdischarge end due to the differential rotation between the conveyor andthe bowl. A stationary slurry feed pipe is centrally located tointroduce the material into the centrifuge. The slurry must, therefore,pas through the conveyor shaft before it gets to the bowl.

Due to requirements of stiffness and strength, the conveyor is generallyfonned of a large hollow tubular shaft. One method of allowing theslurry to pass therethrough has been to use simple round openings in theshaft. This results in a concentrated stream of slurry passing into thebowl. In operation a layer of the solid material forms on the bowlsurface underlying the slurry at any given time. This layer of solidshas been found effective in improving the balance of the centrifuge andin promoting the separation of the very fine particles. It is believedthat this buildup inherently reduces the clearance and therefore leakagebetween the rotating conveyor helix and the rotating bowl. The stream ofslurry from these round openings has been found to create such an impactin the bowl that it disturbs this underlying layer of solids so thatseparation in a centrifuge is reduced with excessive solids beingcarried into the liquid effluent.

Tubular noules either extending radially outward from the shaft orgenerally tangent to the shaft have been added in some designs to reducethis turbulence These nozzles operate to increase the angular speed ofthe discharge through shaft to a lower relative velocity when the streamstrikes the pool in the bowl. This has been effective to increasestability of the centrifuge and improve its separating performance.

Extensive wear has occurred on these nozzles particularly on thetrailing edge where most of the solids in the slurry would tend toconcentrate. This has resulted in the trailing edge of the nozzleswearing through, requiring shutdown and replacement. The use of hardenedmaterial in the nozzles would slowdown the wear, but it is veryexpensive to form these hardened materials in the shape of nozzles andto fasten them securely to the shaft when they must withstand the forcesdue to the high rotating speed.

Since the slurry is dumped in the inside of the rotating shaft of theconveyor, extensive wear occurs as the solid materials slidecircumferentially along the interior surface of the shaft. This createsa wear problem at this location which is critical, since thinning of theshaft would decrease its stiffness and strength. This cannot betolerated in view of the high speed and high forces which occur in alarge centrifuge.

SUMMARY In my invention the opening through the conveyor shaft throughwhich the slurry flows is rectangular in shape, or at least has thetrailing edge generally linear and parallel to shaft axis. A similarlyshaped orifice plate of hardened material may be fastened inside theshaft and sealed around the edges, thus forming a darn around theopenings. The trailing edge of the orifice plate overlaps the openingthrough the shaft.

The use of the rectangular orifice plate and the straight trailing edgespreads the flow of slurry evenly across the orifice opening. Thisresults in a wider, less concentrated stream of slurry into the bowlwhich causes only surface disturbance of the material in the bowlavoiding the penetration that occurs when a round opening is used. Thestraight edge also avoids the concentration of solids in one location sothat wear is spread uniformly across the orifice plate. While in atubular outlet under transverse acceleration, a rotational flow throughthe cross section of the pipe is set up increasing wear. This does notoccur with a rectangular opening.

The orifice plate is simply mounted on the inside of the shaft with thecentrifugal force of rotation helping to keep the orifice plate againstthe shaft. The trailing edge of the orifice can overlap the orificeopening at the trailing edge of the opening. In this manner most, if notall, of the wear occurs on the orifice plate which is made of a hardenedmaterial with minimal wear occurring in the shah.

The orifice plate can be sealed around the opening so that it forms adam within the shaft. This results in a pool of slurry building upinside the shaft which rotates at the speed of the shaft. The slurrybeing added meets this rotating pool rather than the shaft itselfthereby avoiding excessive erosion of the shaft material. The rotatingpool, however, serves to accelerate the slurry being fed toward thespeed of the shaft thereby achieving some angular velocity before thedischarge through the orifice into the bowl.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a general arrangement of acentrifuge;

FIG. 2 is a detailed sectional side elevation in the area of theopenings through the conveyor shaft;

FIG. 3 is a side sectional view of the orifice plate opening through theshaft; and

FIG. 4 is a plan view of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Within casing 12 of thecentrifuge a slurry of water and coal is supplied through centrallylocated slurry feed pipe 13. The slurry is discharged through theopening I4 and ultimately reaches the interior of rotating bowl l5.Water is discharged through opening [7 and discharge spout 18. Thesolids which are separated from the slurry are urged in the oppositedirection passing outwardly through opening 19 and pipe 20.

This longitudinal movement of the solids is accomplished by use ofrotating conveyor 22. While the bowl 15 is rotating at about 1,000 rpm,the conveyor shaft is rotating at only L0 1 0 rpm. This differentialrotation of IO revolutions per minute operates to urge the solid coalparticles towards the discharge end by means of the helical flights 23.These helical flights are mounted on a generally impervious tubularframe 24 of the conveyor.

Discharge from the slurry feed pipe 13 passes to the rotating bowlthrough the rectangular openings 27 in the shaft. Four of these openingsare located around the periphery of the shaft at different longitudinalpositions. Each of the openings occurs at a location between thelocations of the flights. Each opening is 4 1% inches in thelongitudinal direction and 3 inches wide with at least the trailing edgebeing parallel to the shaft axis. Since the rotating shaft must be stiffin order to maintain the clearance between the flights and the bowl andmust also be strong due to the high forces encountered, the materialremoved from the shafl should be minimized. The length of the openings,therefore, is relatively large with the 4 inch openings amounting toover two-thirds of the distance available between flights. The slurryflows out along the trailing edge of the opening of this rotating shaft.Therefore, a 4 inch wide stream flows from each opening into the bowl.By spreading this stream out into 4 inch wide streams, a relatively thinstream is formed at each location so that impact in the bowl isminimized.

Inside each opening in the shafi an orifice plate 28 is mounted. Thisplate may be of alumina or any other wear resistant material. Theopening in the orifice plate is also 4 inches long but only 2 Vi incheswide with the trailing edge 29 of the plate overlapping the opening inthe shaft by V2 inch. Referring to FIG. 3 since the rotating bowl 24 ismoving at high speed to the leh, the relative direction of dischargethrough the openings would be upwardly and to the right. The overlap ofthis orifice plate prevents excessive wear from occurring on therelatively soft material on the shaft so that essentially all wearoccurs on the orifice plate itself.

Since it is very difficult to form complicated shapes of a hardenedmaterial, a relatively simple form is used. The orifice plate ismaintained in place by the use of holddown plates 30 which overlap theorifice plate 30 and are bolted to the shaft with bolts 32. These boltspass from the outside of the shaft so that no wear occurs on the head ofthe bolts. Centrifugal force tends to maintain the orifice plate inposition while the centrifuge is in operation. A rubber gasket 33 isplaced between the orifice plate and the shaft. This soft gasket notonly reduces breakage of the relatively brittle orifice plates in theevent of a slight mismatch of surfaces but also effectively sealsagainst leakage between the orifice plate and the shaft. The orificeplate operates as a dam so that a rotating pool of slurry is formedinside the conveyor shafi. Flow passing from the slurry pipe 13 into theinterior of the shaft impinges on this pool rather than on the shaftitself so as to avoid excessive sliding and wear of the shaft. Therotating pool, however, operates to accelerate the slurry being fed toan angular velocity approaching that of the conveyor shaft so as toreduce the relative velocities when the slurry passes onto the bowl.

While I have illustrated and described a preferred embodiment of myinvention it is to be understood that such is merely illustrative andnot restrictive and that variations and modifications may be madetherein without departing from the spirit and scope of the invention. Itherefore do not wish to be limited to the precise details set forth butdesire to avail myself of such changes as fall within the purview of myinvention.

What I claim is:

l. A centrifuge for separating a slurry into its solid and liquidcomponents comprising: a centrally located slurry feed pipe; a rotatingbowl concentric with said feed pipe; a rotating conveyor within saidbowl and concentric of said slurry feed pipe which rotates at a speedslightly different than said bowl, said conveyor having a generallyimpervious tubular shaft and having on the outer portion of said shahmeans to urge solids longitudinally along said bowl; said feed pipefeeding slurry to the interior of said shaft at a feed location; saidshaft having openings therethrough in the area of the feed location; andsaid openings having at least a trailing edge generally linear andparallel to the axis of said shafi.

2. An apparatus as in claim 1 wherein said openings are rectangular.

3. An apparatus as in claim 2 having rectangular orifice membersfastened inside said shaft at the location of said openings.

4. An apparatus as in claim 3 wherein said orifice members are fastenedto the inside of said bowl in a fluidtight manner whereby the orificeefiectively forms a darn resulting in a rotating pool of slurry withinsaid shaft.

5. An apparatus as in claim 3 wherein said orifice members overlap saidopenings on the trailing edge thereof.

6. An apparatus as in claim 5 wherein said orifice openings have alength longitudinal to the shaft greater than the width of the opening.

7. An apparatus as in claim 6 wherein said openings are longitudinallyoffset relative to one another.

8. An apparatus as in claim 1 having orifice members fastened insidesaid shah at the location of said openings, said orifice having at leasta trailing edge generally linear and parallel to the axis of said shaft.

9. An apparatus as in claim 8 wherein said orifice members are fastenedto the inside of said bowl in a fluidtight manner whereby the orificeeffectively forms a dam resulting in a rotating pool of slurry withinsaid shaft.

10. An apparatus as in claim 8 wherein said orifice members overlap saidopenings on the trailing edge thereof.

II. An apparatus as in claim I wherein said openings are longitudinallyofi'set relative to one another.

I. i i i

1. A centrifuge for separating a slurry into its solid and liquid components comprising: a centrally located slurry feed pipe; a rotating bowl concentric with said feed pipe; a rotating conveyor within said bowl and concentric of said slurry feed pipe which rotates at a speed slightly different than said bowl, said conveyor having a generally impervious tubular shaft and having on the outer portion of said shaft means to urge solids longitudinally along said bowl; said feed pipe feeding slurry to the interior of said shaft at a feed location; said shaft having openings therethrough in the area of the feed location; and said openings having at least a trailing edge generally linear and parallel to the axis of said shaft.
 2. An apparatus as in claim 1 wherein said openings are rectangular.
 3. AN apparatus as in claim 2 having rectangular orifice members fastened inside said shaft at the location of said openings.
 4. An apparatus as in claim 3 wherein said orifice members are fastened to the inside of said bowl in a fluidtight manner whereby the orifice effectively forms a dam resulting in a rotating pool of slurry within said shaft.
 5. An apparatus as in claim 3 wherein said orifice members overlap said openings on the trailing edge thereof.
 6. An apparatus as in claim 5 wherein said orifice openings have a length longitudinal to the shaft greater than the width of the opening.
 7. An apparatus as in claim 6 wherein said openings are longitudinally offset relative to one another.
 8. An apparatus as in claim 1 having orifice members fastened inside said shaft at the location of said openings, said orifice having at least a trailing edge generally linear and parallel to the axis of said shaft.
 9. An apparatus as in claim 8 wherein said orifice members are fastened to the inside of said bowl in a fluidtight manner whereby the orifice effectively forms a dam resulting in a rotating pool of slurry within said shaft.
 10. An apparatus as in claim 8 wherein said orifice members overlap said openings on the trailing edge thereof.
 11. An apparatus as in claim 1 wherein said openings are longitudinally offset relative to one another. 